This invention relates to power conversion systems and more specifically to a current sensing system for use in D.C. power supplies having a predetermined volt-ampere output characteristic.
"Power Conversion Systems" is used in this specification to denote various types of power supplies and other types of systems wherein the principle of this invention would apply, and is not used to limit the application of the subject invention.
Conventional power conversion systems are frequently designed to provide a predetermined volt-ampere output characteristic, despite changes in the load resistance. These types of systems therefore require sensing of the system output voltage and current so that the system operation can be appropriately adjusted to maintain the desired output characteristic. Some systems also require sensing of the output current for safety reasons so that in the event output current rises above a predetermined safe level, the system is turned off.
This current sensing function is usually accomplished by providing a shunt resistor in an appropriate part of the circuit, usually near the output. However, this alternative has several drawbacks. One problem is that the shunt is usually subjected to high current levels because of its location in the circuit. As a result, the shunt resistor and the associated electronic elements for determining the current through the resistor must be designed so that they can withstand the high current and voltage levels at that point in the circuit. These components will also often use a fair amount of the system's power output available. Using high power elements also necessarily increases the production cost of such a system.
Ideally, a current sensing system should be designed so that the more economical low power and low tolerance components can be used, without unduly complicating the circuit and without reducing its reliability and accuracy.